Furnace seal

ABSTRACT

An improved furnace seal comprising a plurality of laterally spaced endless skirts immersed in a liquid trough and including means for supplying a gaseous medium to the spacing between skirts.

United States Patent [191 Blazewicz et al.

[451 Sept. 10, 1974 FURNACE SEAL [75] Inventors: Andrew J. Blazewicz, Barberton;

Edward J. Piaskowski, Massillon; James F. Wood, Stow, all of Ohio [73] Assignee: The Babcock & Wilcox Company,

' New York, NY.

[22] Filed: July 11, 1973 [21] Appl. N0.: 378,293

[52] US. Cl. 110/165 R, 110/171 [58] Field of Search 110/49, 165 R, 171; 122/235 N [5 6] References Cited UNITED STATES PATENTS 2,594,976 4/1952 Mytling 110/165 3,580,226 5/1971 Blackburn, Jr. et al. 1 10/49 X Primary Examiner-Kenneth W. Sprague Attorney, Agent, or Firm-Joseph M. Maguire, Esq.; Robert .1. Edwards, Esq.

[57] ABSTRACT An improved furnace seal comprising a plurality of laterally spaced endless skirts immersed in a liquid trough and including means for supplying a gaseous medium to the spacing between skirts.

10 Claims, 6 Drawing Figures Y PAIENTEDSEPWBN 3.334.323

SHEET 1 0F 3 FIG.1

PATENTED 1 01974 sumanra PAIENTEDSEPWQN 3.834.328

saw an: 3

FURNACE SEAL BACKGROUND OF THE INVENTION The present invention relates to vapor generating units and more particularly to an improved furnace seal arrangement. Large vapor generating units, such as those operated by public utilities, include furnaces for burning ash bearing fuels and are formed with floor openings which discharge the ash, in its solid or liquid state, into a hopper or slag tank located beneath the furnace. Vapor generating units are either suction or pressure fired, the former being of the type wherein the combustion gases contained in the furnace are operated at lower than atmospheric pressure while the latter define operation at higher than atmospheric pressure. A seal is provided between the ash hopper and the furnace so as to prevent the leakage of air into a suction fired furnace or the leakage of combustion gases out of a pressure fired furnace.

The furnace of a large vapor generating unit is topsupported, that is to say the tubular boundary walls associated therewith have their upper ends connected to hangers which attach to structural steel to provide a fixed support. The ash hopper or slag tank is bottomsupported, that is to say it rests on a foundation at ground level or is supported thereon by means of stanchions. As the unit is brought up to operating temperature the furnace wall tubes undergo thermal expansion in a downward direction from the point of restraint at the hangers; conversely, thermal expansion, if any, experienced by components of the ash hopper or slag tank will be in an upward direction from the point of restraint at the base. Thus it can be readily seen that any furnace to ash hopper seal arrangement must be capable of accommodating a difference in magnitude and direction of thermal expansion and contraction between the furnace and the ash hopper. A seal arrangement of the type which has gained wide commercial acceptance was described in U.S. Pat. No. 2,275,652 issued on Mar. 10, 1942 to Harold R. Purcel. The invention therein disclosed includes a trough of water on the outside of and near the top of the ash hopper and a metal sheet having its upper end attached to the furnace and a lower portion submerged in the water contained within the trough.

A serious problem encountered with the above furnace seal arrangement is the limited use life of the metal skirt associated therewith. The failure of the skirt is due to metal wastage which results from the formation of acidic condensate on the. inside surface of the metal sheet. The corrosive condensate may contain both sulphuric and sulphurous acids over a wide range of concentrations. Sulphuric acid occurs when some of the sulfur dioxide in the flue gas is converted to sulphur trioxide, which, in turn, raises the dew point temperature at the metal sheet and condenses thereon to form a high concentration of sulphuric acid. Sulphurous acid occurs when some of the sulphur dioxide in the flue gas diffuses in the corrosion zone and is absorbed by the moisture film which covers the metal sheet.

The problem of metal wastage has been encountered with both suction and pressure fired units; however, it has been most prevalent on the pressure fired units. In

the single seal skirt arrangement of the present state of i the art as applied to a pressure fired vapor generator, there are two water levels in the trough with the lower water level being on the gas side of the seal skirt. With this arrangement, the metal exposed to the flue gas is continuously being cooled by the outside water level thereby providing a condensing surface that combines with certain sulphur compounds in the combustion gases to form acidic solutions which corrode the seal skirts. Since the fuel contributes the sulfur, a change of fuel and/or method of firing may change the sulphur compound concentrations in the flue gas and vary the dew point temperatures as well as the acid strength. Under these conditions no commercially used metal will successfully resist the wide acid concentration and temperature conditions imposed on the seal skirt.

SUMMARY OF THE INVENTION The present invention 'is directed at an improved furnace seal arrangement wherein the problem of seal skirt metal wastage has been substantially eliminated.

Accordingly, there is provided an improved arrangement for sealing the space between the furnace bottom outlet and the inlet to the ash hopper associated there with. The improved seal comprises a liquid trough extending around the outer periphery of the ash hopper inlet and a plurality of laterally spaced endless skirts depending from the furnace bottom and extending into the liquid within the trough and cooperating therewith to preclude leakage therethrough. A heated gaseous medium, preferably air, is supplied to the spacing between seal skirts to maintain the skirt metal temperatures above the dew point temperature thus eliminating the condensation which has caused the formation of corrosive acid solutions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagramatic sectional side elevation view of a steam generating unit embodying the invention.

FIG. 2 is a detail partial sectional side view of an embodiment of the invention.

FIG. 3 is a fragmented front sectional view of the arrangement shown in FIG. 2.

FIG. 4 is a detail partial sectional side view of an alternate embodiment of the invention.

FIG. 5 is a detail partial sectional side view of another alternate embodiment of the invention.

FIG. 6 is a detail partial sectional side view of still another alternate embodiment of the invention.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS The furnace to ash hopper seal of the present invention is illustrated with respect to a vapor generator having a pressure fired furnace. However, it is to be understood that this furnace to ash hopper seal is equally well adapted for use with a vapor generator having a suction fired furnace.

Referring to FIG 1 there is shown a vapor generating unit 10 including an upright furnace chamber 12 comprising fluid heating tubes 14 arranged to form a gastight boundary. Furnace chamber 12 is of substantially rectangular horizontal cross section defined by a front wall 16, a rear wall 18 and side walls 20. The upper end of the furnace chamber 12 is divided into an uptake gas pass 24 and a down-flow or rear gas pass 26. The rear wall tubes are alternately arranged to form the front and rear boundaries of the downflow gas pass 26 and include an upper screen section 28 and a lower screen section 30. The furnace roof 32 is formed by inwardly inclined segments of the front and rear walls 16 and 18 which thence project vertically upward for vapor-fluid discharge into a drum 34. The furnace floor 36 is formed by inwardly sloped segments of the front and rear walls 16 and 18 which thence form a furnace discharge opening 38 and bend outwardly to connect to respective supply headers 40 in fluid receiving communication therewith. Gas passes 24 and 26 will normally contain superheater, reheater and other heating surfaces (not shown). The fuel firing equipment consists of independently operable fuel burners (not shown) extending horizontally along the center line of burner ports 42 which are located in the front and rear walls 16 and 18 at the lower portion of furnace chamber 12. A hot air duct 44 (partially shown) connects to the windboxes 46 to supply combustion air to the burners from a forced draft fan (not shown). A hot gas duct 48 (partially shown) connects to the gas pass 26 at the screen 30- to receive the outflow therefrom for passage to an air heater and stack (not shown).

The vapor generating unit is top-supported by structural steel members including upright columns 50 and cross beams 52. The support for the unit is provided by a plurality of hangers 54 extending downwardly from the beams 52, some of which rigidly attach onto the furance roof 32 while others connect to a cradle which supports the drum 34. The weight of the vapor generating unit 10 is transmitted through the hangers 54 and through the beams 52 to the upright support columns 50 which rest on the ground denoted as G. The tubes 14 have their fixed points with respect to thermal expansion at the hanger connections and will thus expand downwardly as the metal is heated to its operating temperature.

The furnace discharge opening 38 communicates with an ash hopper 56, the latter being situated beneath the floor 36 for receiving ash, slag or scale being discharged from the furnace. The ash hopper 56 will normally include a refractory lined metal casing 58 having an inwardly sloped floor 60 and aroof 62 formed with shoulder portions 64 and a neck 66 defining an inlet opening 68 which is aligned with the furnace opening 38 and is adequately spaced therefrom to accommodate the thermal expansion of the vapor generating unit 10. The ash hopper 56 is supported by a plurality of stanchions 70 which rest on the ground G. A discharge trough 71 extends along the apex of the floor 60 and provides the means for removing the combustion residue collected in the ash hopper 56. Water jets (not shown) are generally used to direct the residue toward the discharge trough 71.

A seal trough 72 rests on the ash hopper roof 62 and is fixedly attached thereto at the shoulder portions 64. The trough 72 is of generally rectangular cross-section and extends as an endless channel around the outer periphery of the ash hopper neck portion 66. The trough 72 is partially filled with a liquid 74, preferably water, which is kept at a level capable of maintaining a seal throughout the operating furnace pressure range of the unit. The water is preferably kept in constant circulation through the provision of inlet and outlet nozzles coupled with a continuous supply of water (not shown).

A plurality of laterally spaced metallic seal skirts depend from the outwardly bent tube segments below the furnace floor 36 and extend at all times, during normal operation, into the water circulating within the seal trough 72 and cooperate therewith to provide a gastight seal between the furnace and ash hopper openings 38 and 68, respectively. Adequate spacing is provided between the skirt surfaces and the trough to accommodate movement due to thermal expansion.

Pressurized heated air is introduced in the space be tween the seal skirts to maintain the metal above the dew point temperature. The heated air is at a pressure higher than the furnace pressure and is taken from the windbox 46 where temperatures average 600 F and is conveyed through a .supply pipe 76 to the spacing between seal skirts. Continuous air circulation between skirts is maintained by providing a vent pipe 78 which discharges to atmosphere. The supply and vent pipes are shown equipped with flow control valves 80 and 82, respectively, to regulate the quantity of heated air circulating between the sea] skirts. It is to be appreciated, however, more elaborate flow control means may be achieved with the addition of such known devices as flow meters, alarms, check valves, etc. Moreover, it will be understood that the supply and discharge points for the heated air may be any suitable source other than that described, e.g. the source of heated air may be the forced draft fan coupled with an indirect heat exchanger and the discharge may be to a scrubbing station associated with the flue gas discharge from the vapor generating unit.

Referring to FIGS. 2 through 6, there are shown detailed views of alternate embodiments of the invention. The following description refers to those elements whichare common to all of the embodiments and is followed by separate descriptions of the elements which are associated with a particular one of each of the embodiments. Accordingly, each embodiment shows a bottom portion of one of the tubes 14 associated with the front wall of the unit, a support plate 84 which extends throughout the width of the front wall and is fixedly connected to the underside of the tubes 14 and scalloped plate members 85 to seal the spaces between the tube webs 15 and the support plate 84. Depending from the support plate 84 and seal-welded thereto are a plurality of laterally spaced skirt plates which extend the entire width of the front wall and are seal-weldably joined with like corresponding plates depending from the rear and side walls to form laterally spaced endless skirts extending along respective planes generally parallel to the plane of the wall associated therewith. The skirt plates are of substantially equal height and have their lower portions immersed in a liquid 74 (preferably water) and cooperate therewith to act as a seal against the flow of gases out of the furnace through the space between the furnace and ash hopper openins 38 and 68, respectively as shown in FIG. 1. The liquid 74 is contained in a trough 72 which is supportingly connected to the ash hopper roof shoulder portion 64.

Referring specifically to FIG. 2, there is shown a detail view of the embodiment of the invention depicted in FIG. 1 comprising an inner skirt plate 86, an intermediate skirt plate 88 and an outer skirt plate 90 spaced from one another and having their respective lower portions immersed in the liquid 74. The supply pipe 76 introduces heated air into the space 92 formed between the inner and intermediate skirt plates 86 and 88, respectively. The air circulates within inner space 92 and exits through a plurality of openings 94 formed in the intermediate skirt plate 88. The air exiting from the space 92 circulates within outer space 96 and is thereafter discharged through a vent pipe 78. The pressure of the heated air is maintained at a value which insures maximum exposure of skirt plate surface within the spaces 92 and 96.

Referring to FIG. 3 there is shown a front sectional view of FIG. 2 including the tubes 14 being weldably joined to one another by gastight web plates 15. The support plate 84 is fixedly connected to the underside of the tubes 14 and has depending therefrom, the skirt plates 86, 88 and 90. The skirt plate 86 is an imperforate plate shown in fragmented section. The skirt plate 88, also in fragmented section, includes a plurality of widely spaced openings 94 having substantially equal dimension preferably situated within the upper half portion of the plate. The skirt plate 90, shown in fragmented section, includes a centrally disposed opening 75 straddled by a pair of openings 77 which are disposed midway the respective ends of plate 90 and opening 75, the openings 77 and 75 being preferably situated along the top portion of skirt plate 90 with opening 75 being of substantially larger dimension than the openings 77. The openings 77 accommodate the passage therethrougl'T of respective vent pipes 78; whereas the opening 75 accommodates the hot air supply pipe 76, the latter passing through alike opening in plate 88. It will be understood that the openings associated with the skirt plates 88 and 90 may vary in size, in number and location depending on the requirements of the furnace seal.

Referring to FIG. 4, there is shown a detail view of an alternate embodiment of the invention wherein the skirt plates comprise an inner plate 86A and an outer plate 90A spaced from one another and having their respective lower portion immersed in the liquid 74. The supply pipe 76 introduces heated air into the space 93A formed between the inner and outer skirt plates 86A and 90A respectively. The air circulates within space 93A and is thereafter discharged through the vent pipe 78.

Referring to FIG. 5, there is shown a detail view of another embodiment of the invention wherein the skirt plates comprise an inner plate 86B and an outer plate 908 spaced from one another and having their respective lower portion immersed in the liquid 74. The supply pipe 76 introduces heated air into a space 93B formed between the inner and outer skirt plates 86B and 90B respectively. The air circulates within space 93B and leaves this space by bubbling through the liquid 74 contained in the trough 72.

Referring to FIG. 6, there is shown a detail view of still another embodiment of the invention wherein the seal plates comprise an inner plate 86C and an outer plate 90C spaced from one another and seal-weldably joined at their respective distal ends to a plate 91C and cooperating therewith to form a gastight space 93C therebetween. The plate 91C as well as the lower portions of the plates 86C and 90C are immersed in the liquid 74. The supply pipe 76 introduces heated air into the space 93C and maintains a positive pressure therein.

It will be understood that for purposes of clarity the illustration and description of the embodiments of the invention have been limited to a showing of the seal plates associated with the front wall of the unit and that these plates are seal weldably joined with like corresponding plates to form laterally spaced endless skirts extending along planes generally parallel to the plane of the wall associated therewith.

While in accordance with the provisions of the statutes there is illustrated and described herein a specific embodiment of the invention, those skilled in the art will understand that changes may be made in the form of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

The embodiments of the invention in which an exclusive property of privilege is claimed are defined as follows:

1. In combination, a furnace chamber having a bottom outlet, a hopper disposed thereunder and including a top opening spaced from said outlet for receiving dis charges therefrom, an improved liquid seal completely surrounding said opening and outlet, said seal comprising a liquid containing trough, plate means depending from the furance bottom and forming a plurality of laterally spaced endless skirts extending into the liquid within said trough, and means for heating the skirts, said heating means including conduit means for supplying heated air to the space between said skirts.

2. The combination according to claim 1 including three laterally spaced endless skirts forming an inner and an outer space therebetween.

3. The combination according to claim 2 wherein the intermediately disposed skirt includes a plurality of conduit means communicating with said outer space for venting the space between said skirts.

6. The combination according to claim 1 including two laterallyspaced endless skirts.

7. The combination according to claim 6 including conduit means communicating with said space for the venting thereof.

8. The combination according to claim 1 including plate means joining the distal ends of adjacent skirts to form a gastight chamber therebetween.

9. A method of sealing combustion gases including a liquid trough, a plurality of laterally spaced endless skirts extending into said trough and comprising the steps of:

maintaining the liquid within said trough at a level wherein each of said skirts has at least the lower end portion thereof immersed in the liquid at all times, and

heating said skirts by applying heated air to the space therebetween.

10. The method according to claim 9 including the step of venting said space. 

1. In combination, a furnace chamber having a bottom outlet, a hopper disposed thereunder and including a top opening spaced from said outlet for receiving discharges therefrom, an improved liquid seal completely surrounding said opening and outlet, said seal comprising a liquid containing trough, plate means depending from the furance bottom and forming a plurality of laterally spaced endless skirts extending into the liquid within said trough, and means for heating the skirts, said heating means including conduit means for supplying heated air to the space between said skirts.
 2. The combination according to claim 1 including three laterally spaced endless skirts forming an inner and an outer space therebetween.
 3. The combination according to claim 2 wherein the intermediately disposed skirt includes a plurality of openings flow connecting said inner and outer space.
 4. The combination according to claim 3 wherein the conduit means communicates with said inner space.
 5. The combination according to claim 3 including conduit means communicating with said outer space for venting the space between said skirts.
 6. The combination according to claim 1 including two laterally spaced endless skirts.
 7. The combination according to claim 6 including conduit means communicating with said space for the venting thereof.
 8. The combination according to claim 1 including plate means joining the distal ends of adjacent skirts to form a gastight chamber therebetween.
 9. A method of sealing combustion gases including a liquid trough, a plurality of laterally spacEd endless skirts extending into said trough and comprising the steps of: maintaining the liquid within said trough at a level wherein each of said skirts has at least the lower end portion thereof immersed in the liquid at all times, and heating said skirts by applying heated air to the space therebetween.
 10. The method according to claim 9 including the step of venting said space. 